This invention generally relates to reproduction of digital artwork. More specifically, the invention relates to software tools for prepress trapping of digital artwork.
Color artwork, which often includes a plurality of graphic or text objects, may be reproduced using any of a variety of different printing processes, including offset lithography, gravure, silk screening, or flexography. For an accurate reproduction of color variations using these methods, two or more different inks are applied, for example, to separate lithographic plates. Generally, three different ink colors (and hence three different lithographic plates) are needed to approximately reproduce the spectrum of colors seen with a human eye. However, in some cases, for example, where only gray tones are needed, only two inks are used; in others, for example, where an especially bright or dark color is desired, more than three inks may be used.
Misregistration, or misalignment during a printing process, is often a problem during printing of color artwork. FIG. 1 illustrates an effect of misalignment during offset lithography. The term xe2x80x9cregistrationxe2x80x9d refers to the precise positioning of color artwork, for example, by exact positioning of a lithographic plate, roller, or screen with respect to a substrate of paper, rubber, or fabric.
As shown in FIG. 1A, when a second color 120 is printed over a first color 110, a darker third color 130 is produced. Thus, in color artwork reproduction, when such a third color 130 is undesirable, the lithographic plate, roller, screen, or other printing device (such as might be used in lithography, flexography, gravure, silk screening, or some other printing process) that is used to reproduce the first color 110 must be modified by xe2x80x9cknocking outxe2x80x9d the first color 110 (FIG. 1B), and the printing device for the second color 120 must be modified by xe2x80x9cbuilding backxe2x80x9d the second color 120 (FIG. 1C). When printing devices are modified as necessary with knockouts and build backs, the second color 120 is reproduced accurately, as shown in FIG. 1D. However, as described above, if the two lithographic plates are misaligned, or if the substrate moves, then the knockout will be slightly offset from the build back, and the substrate (for example, white paper) will show along one edge of the artwork with the darker color 130 appearing along the opposite edge. (See FIG. 1E.)
The problem of misregistration may be alleviated by the use of xe2x80x9ctrapsxe2x80x9d. Traps include xe2x80x9cspreadsxe2x80x9d, xe2x80x9cchokesxe2x80x9d, and are also known as xe2x80x9cclipsxe2x80x9d to some skilled in the art. A spread is an object that has been expanded outwardly (or xe2x80x9cspreadxe2x80x9d) into a surrounding background. A xe2x80x9cchokexe2x80x9d is a background that has been stretched inwardly (or xe2x80x9cchokedxe2x80x9d) into an object surrounded by the background. Traditionally, when knockouts and build backs were hand-cut by a master lithographer, chokes and spreads were applied optically by placing a transparent sheet of high index of refraction material between a film negative of a piece of artwork and the knockout or build back. More recently, as computer-aided printing processes have been developed, computer software has been used to apply spreads or chokes to digital artwork in preparation for printing with multiple inks. Commercial prepress software packages, such as Esko-Graphics Barco(trademark) or Artwork Systems Artpro(trademark) are currently available for applying traps to finished artwork. However, the use of such commercial software packages for prepress processing, including the application of color traps, has distinct disadvantages.
Some disadvantages to the use of such commercial software packages for prepress work include the need for file format conversions. The file format of artwork submitted for prepress work is usually different from the file format used by prepress software packages. Finished artwork is usually produced using an artwork production software package, such as Adobe Illustrator(trademark) or Macromedia Freehand(trademark), and must be converted from the file format used by the artwork production software into the file format for the prepress software package before prepress processing can be completed. File conversion errors often result.
Other disadvantages of file conversion include an inability of artists to make even minor changes to artwork already submitted for prepress processing. Thus, artwork usually goes through a long approval process before being submitted for prepress processing. Changes after submission may be costly or impossible. A minor change to a small aspect of artwork submitted for prepress processing may require a large amount of additional work to correct. For example, if a company wishes to make a slight alteration to a text object, the prepress processing might have to be entirely redone. Jobs are often submitted for prepress processing in batch mode so that a single correction to a trap placed on an object cannot be made without reprocessing of the entire job.
An additional disadvantage to the use of such proprietary file formats and software packages is that prepress software packages require extensive training. Hence, additional company resources (beyond those necessary for simply creating artwork) are required for artwork to be prepared for printing. A smaller company might be unable to afford printing of high quality artwork for advertisements or product packaging simply because prepress processing is unaffordable.
Attempts have been made to improve the accuracy and efficiency of trap placement by transferring digital artwork from the native artwork production environment to a server used for digital prepress processing. In systems of this kind (such as the Esko-Graphics TrapX(trademark) system), a piece of digital artwork (such as an Adobe Illustrator(trademark) file) is transferred to a server, which automatically applies traps to text and graphic objects within the file before transferring the file back to the native artwork production environment. Disadvantageously, file conversions (as described above) may be necessary. And although this conventional technique may allow for trap placement criteria to be specified within the native artwork production environment, the traps themselves are applied on a server, outside the native artwork production environment, which creates additional disadvantages.
Disadvantageously, when a server is used, prepress processing is done in batches: all traps needed for a piece of digital artwork are applied (or reapplied) before transfer back from the server. If an error is found by a user within the native artwork production environment, the piece of digital artwork must be resubmitted and reprocessed. Thus, such conventional systems suffer from many of the disadvantages described above (including, for example, the need for file conversions), and may present additional disadvantages in terms of time needed for transfer of large files back and forth through a network, or cost, for example, of purchasing a server and network hardware.
Yet other disadvantages of previous prepress trapping techniques include inefficiencies within prepress software packages for applying traps. Trapping is currently done manually using some commercially available software packages. Each text object or graphic object in a piece of artwork that requires trapping must be processed separately, requiring a specific sequence of steps to be accomplished before a spread or choke is applied. A single object may not require much time, but when thousands of such objects within a single piece of artwork must be processed in this way, methods of manual trap placement are inefficient.
There is, therefore, a need for an efficient prepress tool for applying accurate, high quality traps to digital artwork within a native artwork production environment.
The present invention meets the foregoing need by providing digital prepress trapping tools designed to function within a native artwork production environment, such as Adobe Illustrator(trademark). The present invention allows for the prepress work of applying high quality traps to be accomplished without conversion to a proprietary file format or transfer of data to and from a server. The trapping tools include tools for automatically generating spreads and chokes according to certain user specified criteria.
Advantageously, in the present invention a digital file of finished artwork that requires prepress processing is trapped within the same software package or application in which it is created (i.e., within the xe2x80x9cnativexe2x80x9d artwork production environment). Spreads or chokes may be applied to every vector art object or text object included in the digital artwork without any file conversion. The invention also allows for a prepress operator to see traps that have been applied within the digital artwork immediately, whereas previous methods for applying quality traps within a host application have required information to be transmitted to and received from a server before traps are displayed.
Using the method and system of the present invention, it is possible for a digital artist to apply traps themselves, removing the need for separate prepress processing of artwork before printing, and allowing for revisions or updates to previously finished artwork to be made more easily than with conventional methods for prepress processing of artwork. In an embodiment, files are not saved in a non-native format or converted to a proprietary software system, and there is no need for files to be reconverted before being viewed by an artist or other user. Furthermore, because the method and system of the present invention may be implemented within a native artwork production environment, the resources required for adequate training in the application of traps to artwork are substantially fewer.
According to the method and system of the present invention, after digital artwork has been approved by a client, the invention is applied in a native artwork production environment, eliminating the need for a conversion of the digital artwork into a different format. After the method of the present invention has been carried out, the digital artwork can be submitted for print processing, for example, as a PostScript format file. The digital artwork submitted is usually received by a Raster Image Processor (RIP) for screen ruling, dot gain analysis, and angle, dot shape or structure assignment. The digital artwork is then sent to an output device, such as a plate or film setter. For gravure printing, the bitmap data is either sent to a digital engraving machine or data is output to film, and engraved on a cylinder. Using the present invention, no prepress trapping outside the native artwork production environment is needed.
In an embodiment, the invention has been implemented as a set of plug-ins for use with Adobe Illustrator(trademark). However, as will be understood by those of ordinary skill in the art, the method and system of the present invention are susceptible to implementation in a plurality of different artwork production environments, for example, in an environment in which the prepress tools are implemented without reference to a previously developed Application Programming Interface (API) or other libraries of software tools. The invention should be understood to include such alternative embodiments since the trapping tools described herein might be implemented by one of ordinary skill in the art in any such alternative embodiments.
In many conventional artwork production software packages, digital artwork is output as a PostScript language file. Hence, much of the terminology used to describe how traps are implemented in the present invention is common to the PostScript programming language. An excellent reference, including a detailed description of some of the PostScript language terms and concepts used in the present application (e.g., paths, Bezier paths, and conventions used with winding algorithms) is publicly available at
http://partners.adobe.com/asn/developer/technotes/postscript.html in the third edition of the PostScript Language Reference manual. The digital prepress trapping tools of the present invention are implemented, in an embodiment, as a plug-in for Adobe Illustrator(trademark), a commercial artwork production software package that has conventionally produced PostScript format output files. However, as described above, other programming languages, page description languages, or scripts might also be used to implement the digital prepress tools of the present invention, for example, in Macromedia Freehand(trademark), Adobe Acrobat(trademark), Adobe In Design(trademark), or Corel Draw(trademark). In general, any language or format in which a piece of digital artwork could be submitted for print processing might be used in accordance with the method and system of the present invention, and the present invention can be used with any digital vector artwork production environment or processing system.
The digital prepress tools of the present invention allow a user to apply traps to vector art objects within a design. The term xe2x80x9ctrapxe2x80x9d as used in accordance with the present invention may refer to chokes or spreads (which are sometimes also known as xe2x80x9cclipsxe2x80x9d) of a piece of artwork, or to a combination of chokes and spreads.
In accordance with the present invention, a xe2x80x9cpathxe2x80x9d is a graphic object specified by logically connecting at least two points in a definite direction. The path may be rectilinear or may be curved as specified, for example, by designating the points as knots in a Bezier path. A path may be xe2x80x9copenxe2x80x9d or xe2x80x9cclosed.xe2x80x9d Closed paths have a well-defined interior portion. Paths may be xe2x80x9cstrokedxe2x80x9d so that the logically connected points in the path are physically connected by lines, or, in cases where paths are closed, xe2x80x9cfilledxe2x80x9d so that the interior portion of the path has a well-defined color. A closed path may be stroked, filled, both, or neither. In addition, closed paths also have an xe2x80x9corientationxe2x80x9d property which is either xe2x80x9cclockwisexe2x80x9d or xe2x80x9canticlockwisexe2x80x9d, depending on whether the logical connections between the points of the path are traversed in a clockwise or an anticlockwise direction. (xe2x80x9cAnticlockwisexe2x80x9d is also known as xe2x80x9ccounterclockwise.xe2x80x9d) The direction of traversal, or xe2x80x9corientationxe2x80x9d property of a path is sometimes needed in determining whether a particular point within a text or graphic object in a piece of digital artwork lies inside or outside a closed path. (See description below.)
xe2x80x9cCompound pathsxe2x80x9d include groups of one or more other paths that are defined as a single graphic object. Paths included in compound paths are called xe2x80x9csubpathsxe2x80x9d. Subpaths may be filled or empty in accordance with their clockwise or anticlockwise orientation and the xe2x80x9cinsideness rulexe2x80x9d being used. With an even-odd winding rule, the inner circle of two concentric circles will always be empty. With a nonzero winding rule, the inner circle may or may not be filled depending on whether the two subpaths are traversed in parallel (both clockwise or both anticlockwise) or antiparallel (a first clockwise and a second anticlockwise) directions. (See the Postscript Language Reference Manual for additional description.) As is known to those of ordinary skill in the art, any kind of digital artwork (including graphics, text, or both) is susceptible to construction from paths or compound paths. Any kind of digital artwork having paths, vectors, or other similar system for specifying the position of text or graphic objects is susceptible to being adapted for use with the trapping tool of the present invention.
Traps are closed, filled, un-stroked paths that modify the geometry of a vector art object. As is known to those of ordinary skill in the art, all objects in a piece of digital artwork (including paths and compound paths) have a well-defined geometry. The geometry of an object can be modified, for example, when a spread or a choke is applied to an entire path, by expanding or contracting the area defined by the path. In the case of a partial spread or a partial choke, or in the case of a spread or a choke to a compound path, the modification is more complicated. (Some more complicated modifications to the geometry of an object are shown by way of example in FIGS. 3A, 3B, 3E, and 3F.) Advantageously, the present invention allows for the geometry of an object to be modified nondestructively, i.e., without destroying or changing the object being trapped. The ability of the present invention to nondestructively modify the geometry of an object is further described below.
As explained above, traps serve to alleviate the problems associated with misregistration in offset lithography. Traps can be logically divided into four portions: (1) an inner side of a trap uses the same points as the path being trapped; (2) an outer side of a trap is parallel to the inner side of the trap, and offset therefrom (in a direction that depends on whether the trap is a spread or a choke) by a user-specified trap width; (3) the two ends of the trap are formed at user-specified angles to the inner side and the outer side of the trap; and (4) the fill for the trap, which is the same as the fill of the path being trapped in the case of a spread, and the same as the fill of the background to the path being choked in the case of a choke.
According to the method and system of the present invention, each of the four logical portions are constructed automatically using software tools within a native artwork production environment. Separate tools are provided for applying a choke to an entire path (xe2x80x9cChoke Allxe2x80x9d), to a portion of a path (xe2x80x9cChoke Partxe2x80x9d), or for applying a spread to an entire path (xe2x80x9cSpread Allxe2x80x9d) or a portion of a path (xe2x80x9cSpread Partxe2x80x9d). In some embodiments, a separate xe2x80x9cOverprintxe2x80x9d tool is also provided for more conveniently specifying how a trap is to be positioned with respect to the object being trapped. In various embodiments, a different subset of these tools may be provided.
When a tool is used, a user provides xe2x80x9cuser specified criteriaxe2x80x9d that defines how traps are applied. User specified criteria includes, in an embodiment of the present invention, a trap width, a mitre limit to the pointiness of corners in the path being trapped, the type of mitre joins or mitre angle, and other information about whether or how partial traps are applied. In an embodiment of the present invention in which the trapping tools are implemented within Adobe Illustrator(trademark), the user specified criteria is entered in a xe2x80x9ctrapping palette.xe2x80x9d Traps are then applied to objects according to the user specified criteria when an object is selected and an appropriate trapping tool within the toolbox is clicked or otherwise activated.
In an embodiment, the trapping palette is displayed as a window in a native artwork production environment, which presents information and requests input. The trapping palette is displayed, in an embodiment, only while trapping tools are available in a toolbox within the native artwork production environment, and may also be called a xe2x80x9cfloating palettexe2x80x9d. Although the embodiment of the present invention shown in FIGS. 2A and 2B includes tools within a toolbox and a trapping palette including numerical fields, pop-up menus, a check box, and a button, it will be understood by those of ordinary skill in the art that a different embodiment might also be implemented, for example, in which the tools are included in a separate dialog box rather than in a toolbox. In addition, a different combination of pop-up menus, checkboxes, option boxes, scrolling lists, slider bars, icons, or buttons might also be used with the present invention, and the system of the present invention should not be understood as limited to the particular embodiment shown in FIGS. 2A and 2B.
According to an embodiment of the present invention, objects within a file of digital artwork are trapped sequentially. After an object has been selected and user specified criteria for the object have been entered (for example, in a trapping palette), an icon for the desired trapping tool (for example, Spread All 2010 in FIG. 2A) is activated, for example, by pressing a hot key or clicking on the tool. The trap is then automatically applied to the selected object. A substantially similar set of steps may be used to apply a Choke All trap to an object within the digital artwork. Spread All and Choke All work automatically with compound paths.
Spread Part 2020 and Choke Part 2040 tools are used in a slightly different way. Again, a single object is selected and user specified criteria are entered, for example, in a trapping palette. However, after entering the user specified criteria and activating either the Spread Part 2020 or the Choke Part 2040 tool, when a user moves his or her mouse over the selected object a numeral xe2x80x9c1xe2x80x9d appears, indicating that by clicking the user will specify a first trap point. Upon clicking once, the numeral xe2x80x9c1xe2x80x9d becomes a numeral xe2x80x9c2xe2x80x9d, indicating that by clicking again a second trap point will be placed. After the second point is set with a second click, a trap is automatically applied to the shortest path along the edge (or outer path) of the object being trapped between the two points. According to an embodiment of the present invention, a separate xe2x80x9cTransposexe2x80x9d button allows for the trapped path to be swapped for the longest path between the two points along the edge of the selected artwork instead. As described below, Spread Part and Choke Part tools also work automatically with compound paths or shapes, grouped paths, or non-compound paths or shapes. An important advantage of the Spread Part and Choke Part tools is that the first and second points can be set at any point along the edge of any kind of object.
The use of hot keys presents an additional advantage of embodiments of the present invention. As an alternative to selecting trapping tool icons, in another embodiment a user presses a xe2x80x9cHot Keyxe2x80x9d on a keyboard. In an embodiment, Hot Key xe2x80x9c1xe2x80x9d activates Spread All, Hot Key xe2x80x9c2xe2x80x9d activates Choke All, Hot Key xe2x80x9c3xe2x80x9d activates Spread Part, Hot Key xe2x80x9c4xe2x80x9d activates Choke Part, Hot Key xe2x80x9c0xe2x80x9d activates the Transpose button, and Hot Key xe2x80x9c5xe2x80x9d toggles (activates or deactivates) an Overprint setting. A user skilled with in the use of such Hot Keys may save a considerable amount of time in applying traps to a plurality of objects within a piece of digital artwork. Other keyboard shortcuts might be used in a different embodiment of the present invention.
In another embodiment of the present invention, trapping tool icons in a toolbar or toolbox might be selected from a single trapping tool icon with a pop-up xe2x80x9cflyoutxe2x80x9d toolbar. Flyout toolbars may be displayed, for example, after a corner of an icon is clicked, or after the mouse has hovered over the icon for longer than a specified interval of time. In yet another embodiment, the trapping tools might be displayed in a free-floating palette, which might accessible by xe2x80x9ctearing offxe2x80x9d a flyout toolbar from the main toolbar in an artwork production environment.
Advantageously, the present invention does not modify or destroy objects trapped in a piece of artwork. In addition, objects are not transferred to a server before being trapped, and trapped are applied without leaving the native artwork production environment. In an embodiment, the objects being trapped remain continuously within the native artwork production environment. As a result, the present invention lessens the need for additional hardware (for example, for expanding the bandwidth of the network used for transferring large graphics files back and forth from a server) and software for prepress processing.
Perhaps more importantly, the present invention does not require prepress processing of objects in a piece of digital artwork to be done in batch; rather, individual graphic or text objects may be modified instantly within the native artwork production environment, and reprocessing of other objects within a piece of digital artwork is unnecessary. Also, because the traps are applied nondestructively (i.e., the original object is not deleted from computer memory), traps already applied to an object may be easily modified or removed, reproducing the original, un-trapped object.